Reducing heat-seal temperature requirements for coatings prepared from latexes of vinylidene chloride polymers

ABSTRACT

A process for reducing the heat-seal temperature requirements of films and coatings produced from high vinylidene chloride polymer latexes comprising having present in films or coatings formed from such latexes, prior to fusion thereof, from about 0.5 to about 5 percent by weight of latex polymer solids of a polyoxyethylene sorbitan fatty acid monoester containing from about 10 to 20 moles of ethylene oxide and wherein said fatty acid contains from about 12 to 18 carbon atoms.

United States Patent I 1191 I Gibbs et a1.

REDUCING HEAT-SEAL TEMPERATURE REQUIREMENTS FOR COATINGS PREPARED FROMLATEXES OF VINYLIDENE CHLORIDE POLYMERS Inventors: Dale S. Gibbs;Ritchie A. Wessling,

both of Midland, Mich.

Assignee: The Dow Chemical Company,

Midland, Mich.

Filed: July 9, 1973 Appl. No.: 377,479

Related US. Application Data Continuation-in-part of Ser. No. 202,625,Nov, 26, 1971, abandoned.

US. Cl. 260/29.6 TA, 260/29.6 E, 260/29.6 MQ, 260/29.6 RB, 260/29.6 RW,260/29.6 SQ, 260/29.6 Z

Int. Cl. C081 l/l3 Field of Search260/29.6 TA, 29.6 E, 29.6 MQ,

Oct. 22, 1974 References Cited UNITED STATES PATENTS 3,309,330 3/1967Settlage 260/291) TA 3,324,064 6/1967 Fikentscher et a1 260/2911 TA3,617,368 11/1971 Gibbs 260/291) TA X 3,639,324 2/1972 Owens Zoo/29.6 TAX 3,701,745 10/1972 Settlage c1111.... Zoo/29.6 TA X PrimaryExaminer-Lucille M. Phynes Attorney, Agent, 0r Firm-Rona1d G. Brookens'1 5 1 ABSTRACT 5 Claims, No Drawings REDUCING HEAT-SEAL TEMPERATUREREQUIREMENTS FOR COATINGS PREPARED FROM LATEXES OF VINYLIDENE CHLORIDEPOLYMERS BACKGROUND This application is a continuation-in-part of thenow abandoned Application Ser. No. 202,625, filed Nov. 26, 197i.

Copolymers and interpolymers of vinylidene chloride with such comonomersas acrylonitrile, vinyl chloride, and lower alkyl acrylates have foundwide acceptance as film and coating materials because of their desirableproperties including transparency, inertness, ability to be heat sealedand impermeability to moisture and gases. It is also recognized that theimpermeability of such film and coatings increases 'wtih an increasingconcentration of vinylidene chloride in the polymer latex. It is furtherrecognized that such increase in impermeability is accompanied by ahigher temperature requirement for producing an effective heat seal inthe resulting film or coating, e.g., film and coatings prepared from apolymer containing at least about 80 percent by weight vinylidenechloride in the polymer molecule requires a temperature of at leastabout 160 C. for effective heat sealing. This high temperaturerequirement is particularly undesirable where high speed commercialpackaging techniques are employed.

It is the primary object of this invention to provide a means ofsignificantly lowering the heat-seal temperature requirement for filmsand coatings prepared from polymers containing at least about 80 percentby weight of vinylidene chloride in the polymer molecule, withoutadversely affecting the impermeability and other desired properties ofsuch film or coatings.

SUMMARY The above and related objects areattained by a processcomprising the production of a polymer latex which consists essentiallyof water and a colloidally dispersed solid polymer prepared by thepolymerization in aqueous dispersion of l. at least about 80 percent byweight based on the total weight of monomers used of vinylidenechloride,

2. from about 0.1 to about percent based on the total weight of themonomers used of a significantly water-soluble ionic materialselectedfrom the group of sulfonic acids and their salts having the formulawherein the radical R is selected from the group con.- sistirig of vinyland alpha-substituted vinyl; the symbol 2 represents adifunctionallinking group which will activate the double bond present insaid vinyl group; Q is a; divalent hydrocarbon having its valence bondson different carbon atoms; the symbol M+ represents a cationselected'from the group consisting of free acids, alkali metalsalts,and' ammonium,amine, sulfonium and quaternary ammonium salts, and

3. any remainder being one or more monoethylenically unsaturatedcomonomers; wherein there is present in thefilms and coatings producedfrom such latexes, prior to fusion thereof; from about-0.5 to about 5percentby weight of polymer solids of a polyoxyethylene sorbitan fattyacid monoester containing-from about 10 to 20 moles of ethyleneoxide andwherein said fatty acid contains from about 12 to 18 carbon atoms. 1 a

it has been unexpectedly discovered, which discovery forms a part of thepresent invention, that the prescribed amounts and types of suchmonoesters, when incorporated in the monomer charge or post-added to thepolymer latex, exude to the surface of film or coatings prepared fromthe disclosed polymer latex as the film or coating fuses andcrystallizes; and that such monoester remains present on such surfacesas heat and pressure are appliedduring conventional heat-sealoperations. Under such applied .heat and pressure, however, thesolubility of the monoester, in' the film or coating, appears to beincreased sufficiently to reduce the temperature required for attainingan effective heat seal, i.e;, excellent heat seals are obtained attemperatures as low. as. C. as contrasted to temperatures of C. or morefor films or coatings absent such monoester-Although the exact mechanismis unknown, it is known that-the comonomeric emulsifier constituent usedin the preparation of the prescribed polymer latexes, although providingsignificantly enhanced latex colloidal stability, also results in higherheat-seal temperature requirements. it appears that the nonionicadditives of this invention interact in some way with such comonomericemulsifier to remove such detrimental characteristic.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The .polymer latexesused in thepresent invention may be prepared in any conventional manner but arepreferably prepared in aqueous dispersion by an essentially continuous,carefully controlled addition of the requisite polymerizationconstituents (including polymerization initiator systems if desired) toan aqueous medium, as-per the techniques set forth in the US. Pat. No.3,617,368, issued Nov. 2, 1971.

More particularly, it is often preferred to first add a small amount ofthe monomeric materials, as defined herein, to the aqueous medium havingthe desired pH value, followed by the subsequent addition of thenecessary polymerization initiator, to form a polymeric seed latex inorder to aid in the control of particle size. Whenforming such polymericseed latexes by the procedure' as described herein, small amounts ofconventional wetting agents such as alkali soaps or the like, may beincorporated in the aqueous medium to further aidin the attainment ofparticles of desired size. The addition of such wetting agents, however,is not critical for the production of the highly stable aqueous colloi-4 As described, supra, the prescribed polymer latexes are prepared froma monomer composition containing at least about 80 percent by weightvinylidene chloride,

and preferably between about weight of such monomer.

The copolymerizable ionic monomer of such polymer latexes are thosemonomeric materials which contain in their structure both an ionizablegroup and a reactive double bond, are significantly soluble in water,

85 and 95 percent by and where the substituent on the double bond ischemically stable under the conditions normally encountered in emulsionpolymerization. Particularly useful are the sulfonic acids and theirsalts which may be described by the formula:

wherein the radical R is selected from the group consisting of vinyl anda-substituted vinyl; where the symbol Z representsa' difunctionallinking group which will activate the double bond present in the vinylgroup, e.g.,' groups of the structure: 1

It is further to be noted that with one of the ions above, and the usualchoices for R and Z, the solubility of the monomer depends on Q. Asindicated, this group can. be either aliphatic or aromatic and its sizewill determine the hydrophilic/hydrophobic balance in the molecule,i.e., if Q is relatively small the. monomer is water solublebut as Qbecomes progressively larger the I surface activity of such monomerincreases until it becomes a soap and ultimately a water-insoluble wax.It is to be understood, however, that the limiting size of Q depends onR, Z and M+. As exemplary of the above, it has been found that sodiumsulfoalkyl methacrylates of the formula:

CH C

l 3 II CH2 C (Cltl S0 Na+ wherein n is 2, are highly acceptablecopolymerizable ionic materials for use in the present invention.

Further, the selection of R and Z is governed by the reactivity neededand the selection of Z is usually determined by the reaction used toattach the sulfonic acid to the base monomer (or vice versa). g

It has been found that sodium sulfoethyl methacrylate is especiallyeffective for use.

Other monomers which readily copolymerize with vinylidene chloride inaqueous dispersion, i.e., which cent at the temperature ofpolymerization, may also be used in preparation of the polymer latexesused in the present invention. Exemplary of preferred materials aremethacrylic acid, methyl methacrylate, hydroxy ethyl and propy]acrylates, hydroxyethylmethacrylate, acrylic acid, acrylonitrile,methacrylonitrile, acrylamide and the lower alkyl anddialkylacrylamides, acrolein, methylvinyl ketone and vinyl acetate.

The polyoxyethylene sorbitan fatty acid ester prescribed by the presentinvention may be added with the monomer charge during preparation of thepolymeric latex-or may be post-added following preparation of the latex,or may be coated on the surface of films or coatings prepared from suchlatexes, prior to fusion thereof.

Exemplary of the polyoxyethylene sorbitan fatty acid esters useful forthe present invention are: polyoxyethylene sorbitan monolauratecontaining from about 10 to 20 moles of ethylene oxide, polyoxyethylenesorbitan monopalmitate containing from about 10 to 20 moles of ethyleneoxide, polyoxyethylene sorbitan monostearate containing from about 10 to20 moles of ethylene oxide, and polyoxyethylene sorbitan monooleatecontaining from about 10 to 20 moles of ethylene oxide. I

The above are nonionic surfactants obtained by esterification ofsorbitol with a fatty acid under conditions which result in thesplitting out of water from the sorbitol leaving sorbitan. Varyingamounts of ethylene oxide are then added to the monoester to control thewater solubility of the product with additional ethylene oxideincreasing the water solubility.

The latexes of the present invention are particularly useful forpreparing coated products comprising a wide variety of substrates havinga continuous, adherent, dried coating of such latex thereon whichcoating has excellent barrier, flexibility, low heat-seal temperaturerequirement and excellent binding capacity properties.

Exemplary of the substrates which may be advantageously coated with thepolymer latexes of this invention are sheets or films of: thenonaromatic hydrocarbon olefin polymerssuch as the polymers andinterpolymers of ethylene, propylene, and butylene and the like andtheir halogenated derivatives; the aromatic hydrocarbon polymers such asthe polymers and interpolymers of styrene and the like; the polyesterssuch as polyethylene terephthalate and the like; various polyamides suchas'polyhexamethylene adipamide among others; polyimides; the halogenatedethylene polymers I such as the vinyl and vinylidene chloridehomopolymers and interpolymers; polyacrylonitrile; regeneratedcellulose; and the various cellulose esters such as cellulose acetate,cellulose nitrate and cellulose acetate butyrate; polyvinyl acetals;vinyl combinations such as polyvinyl chloride/polyvinyl acetatecopolymers; fibrous cellulosic materials such as tissue paper, bookpapers, crepe paper, wrapping paper, cardboard, chipboard, wallboard andthe like; metals such as aluminum and tin, among others; wood productssuch as plywood; textiles such as cotton textiles and fabrices; othervegetable fiber products; and other substrata which are relativelyinsoluble in the coating dispersions of the present invention. it is tobe understood that the polymer latexes described herein can also be usedto cast unsupported films or sheets if desired.

The following examples illustrate the polymer latexes and preparation ofcoated products therefrom according to this invention, but are not to beconstrued as limiting its scope. in the examples, parts and percentagesare by weight unless otherwise indicated. 5 topcoat of a soft vinylidenechloride polymer. Each coated sample was then aged at 140 F. for aperiod of EXAMPLE 1 about l6 hours to permit crystallization of theappliedinto a polymerization vessel was charged a mixture of vmylldeneChlonde latex- After agmg heal-seal 500 grams of deionized water(adjusted to pH of 3.5 f h coated Sample were determined, (J withglacial acetic acid) and 2.5 grams of sodium dode- P mch h after eachcoated sample h mdlvlfiu' cyl benzene sulfonate. To this mixture wassubseany been subficted to a P of 20 P for a Perlod quently added aninitial monomer charge comprising of 1 second Pnder normal room temperatureS 46 grams of vinylidehe chloride 4 grams of acryloni Theemulsifiers used have the following designations trile and 0.05 gramst-butyl hdyroperoxide. and structures:

The reaction mixture was then stirred under nitrogen for a period ofminutes at a temperature of C., Emulsifier and a solution comprising 2.7grams of sodium formal- De g at on t cture dehyde sulfoxylate 111 500grams aqueous solution was A Sodium 53 of dodecylbenzene Home thereafteradded to the reaction mixture at a rate of 7.7 B Sodium lauryl sulfategrams of solution Per hour until polymerization of the 20 C gf ggfg z gginitial charge of monomers was completed. Following D p x ne S r n m iar completion of polymerization of the initial charge of Commmng 20 moleso ethylene OXlde E Polyoxyethylene sorbitan monooleate monomericmaterials, a second monomeric mixture containing 20 moles Methyleneoxide comprising 1,012 grams of vmylrdene chloride, 88 25 grams ofacrylonitrile and 1.1 grams of t-butyl hydroperoxide was added to thepolymerization vessel with The following Table I sets forth the typesand stirring at a rate of 55 grams of the mixture per hour for amountsof emulsifiers used and the heat-seal values a period of 20 hours. Overthe same period of time, a obtained. v

TABLE I Exp. No. Emulsifier Heat Seal (GmsJin. width) Type Amount 1 10C.120C. 130C.

(% by weight of polymer solids) For Comparison 1 None 0 0 0 2 A 0.5 5 e18 3 A 1.0 5 8 l6 4 B 0.5 4 5 8 5 B 1.0 6 c 0.5 2 6 24 7 c 1.0 2 6 16The invention "s' D 0.5 10 4s 51 9 D 1.0 14 146 Substrate tear 10 E 0.56 18 51 'l l E 1.0 40 I03 Substrate tear tions, to individual portionsof the polymer latex and each admixture allowed to stand overnight. Theadmixtures were then each coated on separate portions of a substratecomposed of glassine paper having thereon a Seal strength exceedsstrength of the substrate.

solution comprising 17.6 grams of sodium sulfoethyl methacrylate in 300grams of aqueous solution was separately added to the polymerizationvessel at a rate of 15 grams of solution per hour. Following theaddition of the polymerizable materials, the herein described aqueoussolution of sodium formaldehyde sulfoxylate was added to thepolymerization vessel at the preestablished rate for a period of twohours, to allow completion of polymerization of the monomericconstituents. The resulting polymerization product was a highlycolloidally stable, low-foaming, aqueous colloidal polymer dispersioncontaining approximately to 52 percent polymer solids prepared from atotal monomer charge of about 92 parts by weight of vinylidene chloride,about 8 parts by weight of acrylonitrile and about 1.6 parts by weightof sodium sulfoethyl methacrylate.

Thereafter, in each of a series of experiments, one of severalemulsifiers were admixed, at varying concentra- The data from Table 1illustrate the significantly enhanced low temperature heat-sealcharacteristics obtained using the emulsifiers prescribed by the presentinvention. In addition, such reduction in heat-seal temperaturerequirements was not accompanied by any observable loss inimpermeability or other desirable properties of the latex coating.

EXAMPLE 2 in two coats. A No. S Mayer rod was used for the first coatand then a No. 8 Mayer rod for the second coat giving a total coatingweight in the range of 5 to 7 pounds per 3,000 ft.*. Each coat was driedfor 10 to 20 wherein the radical R is selected from the group consistingof vinyl and alpha-substituted vinyl; the symbol Z represents adifunctional linking group of the strucure water-soluble ionic materialselected from the group of sulfonic acidsand their salts having theformala l seconds in a forced air oven operating at a temperature 5 O oof about 250 to 300 F. The minimum heat-seal temn 9 9 1 perature(MHST)was determined by separately sealing -1 fl w l-inch wide strips ofcoated material at varying temperatures using a 10 to 20 PSI heat sealerjaw pressure and which will activate the double bond present in said to1 second dwell time. The MHST was determined vinyl group; -Q- is analkylene and arylene divalent as that temperature required to causecomplete fiber hydrocarbon having from one to about eight carbon tear ofthe seal as it was pulled apart on a Scott X 5 tenatoms and having itsvalence bonds on different carbon sile tester. atoms; the symbol M+represents a cation selected The following Table-ll sets forth thepresence or abfrom the group consisting of free a alkali ta sence of thesulfonic acid salt and the polyoxyethylene l5 Salts, and ammonium,amine, SulfOnium and q a ernary sorbitan fatty acidvmonoester, as wellas the minimum ammonium Salts, and heat-seal temperature Ml-1ST) of eachcoated sample. any tsm being UQ QDQ F Yl TABLE 11 Sulfonic AcidEmulsifier MHST Sample No. Salt by wt.) by wt) (type) (C.)

- For Comparison 12 none none none I40 13 none 3 (D) 130 14 none 3 (E)150 15 L4 none none 140 The Invention 1.4 5 (D) 100-105 17 1.4 3 D100-110 18 1.4 1 (D) 110-120 19 1.4 1 (E) 110-120 Series B nicallyunsaturated 'comonomers selected from the The experiments as describedin Series A above were group consisting of methacrylic acid, methylmethrepeated utilizing a polymer latex, the polymer solids of acrylate,hydroxyethylacrylate, hydroxypropylawhich were prepared from a monomercomposition of crylate, -hydroxyethylmethacrylate, acrylic acid, about 0Part y W g inyli bout l5 acrylonitrile, methacrylonitrile, acrylamideand the parts by weight butylacrylate, about 5 parts by weight loweralkyl and dialkylacrylamid'es, acrolein, methacrylonitrile and about 1.6parts by weight of sodium ylvinyl ketone and vinyl acetate, said processcom- ,sulfoethyl methacrylate. The following Table III sets prising:having present in said polymer latex prior forth the presence or'absenceof the sulfonic acid salt 40 to fusion of said latex into a film orcoating from and the alkyl phenol olefin oxide ,adduct, as well as theabout 0.5 to about 5 percent by weight of latex minimum heat-sealtemperature (MHST) of each polymer solids of a polyoxyethylene sorbitanfatty coated sample. y H 1 acid monoester containing from about 10 to 20TABLE 111 I .Sulfonic Acid Emulsifier MHST Sample No. Salt by wt.) bywt) (type) (C.)

For Comparison I 20 1.6 none none I lO-l 15 The Invention T 1.6 5 (D)90-95 22 I 1.6 3 (D) 90-95 What is claimed is; moles of ethylene oxideand wherein said fatty acid l. A process for reducing the heat-sealtemperature Contains frOm a out 12 to 13 carbon atoms. requirements offilms and coatings produced from a The p p clam} Sald slgmficamlypolymer latex hi h latex consists essentiafly f water water-soluble1on1c mater1al 15 sodium sulfoethyl methand a colloidally dispersedsolid polymer prepared by y mthe polymerization in aqueous dispersion ofT Process f Claim whel'em the m at least abcm 80 percent by weight basedon the used in the preparation of said polymer latex are v1nyl1- totalweight f monomers used f vim/dene ch]o dene chloride, acrylonitrile andsodium sulfoethyl ride, and methacrylate. v v 2. from about 0.l to about5 percent based on the The Process of clam 3 wherem Polymer latex totalweight of the monomers used of a significantly Prepared f mPnomercomposition of about 92 parts by weight v1nyl1dene chloride, about 8parts by weight acrylonitrile and from about 1.4 to 1.6 parts by weightsodium sulfoethyl methacrylate.

5. The process of claim 3 wherein said polymer latex is prepared from amonomer composition of about 3 ,843 ,5 8 l 9 10 p gi t by weight fih ytifl epe hloride, about parts by trile and about 1.6 parts by weight ofsodium sulfoethyl Wi h PEY!FEFY1F1P9P5.P?E by weight a xlsm amethacrylate-

1. A PROCESS FOR REDUCING THE HEAT-SEAL TEMPERATURE REQUIREMENTS OFFILMS AND COATINGS PRODUCED FROM A POLYMER LATEX WHICH LATEX CONSISTSESSENTIALLY OF WATER AND A COLLOIDALLY DISPERSED SOLID POLYMER PREPAREDBY THE POLYMERIZATION IN AQUEOUS DISPERSION OF
 1. AT LEAST ABOUT 80PERCENT BY WEIGHT BASED ON THE TOTAL WEIGHT OF MONOMERS USED OFVINYLIDENE CHLORIDE, AND
 2. FROM ABOUT 0.1 TO ABOUT 5 PERCEBNT BASED ONTHE TOTAL WEIGHT OF THE MONOMERS USED OF A SIGNIFICANTLY WATERSOLUBLEIONIC MATERIAL SELECTED FROM THE GTOUP OF SULFONIC ACIDS AND THEIR SALTSHAVING THE FORMULA
 2. The process of claim 1 wherein said significantlywater-soluble ionic material is sodium sulfoethyl methacrylate.
 2. fromabout 0.1 to about 5 percent based on the total weight of the monomersused of a significantly water-soluble ionic material selected from thegroup of sulfonic acids and their salts having the formala R-Z-Q-SO3 -M+wherein the radical R is selected from the group consisting of vinyl andalpha-substituted vinyl; the symbol Z represents a difunctional linkinggroup of the structure
 3. any remainder being one or moremonoethylenically unsaturated comonomers selected from the groupconsisting of methacrylic acid, methyl methacrylate,hydroxyethylacrylate, hydroxypropylacrylate, hydroxyethylmethacrylate,acrylic acid, acrylonitrile, methacrylonitrile, acrylamide and the loweralkyl and dialkylacrylamides, acrolein, methylvinyl ketone and vinylacetate, said process comprising: having present in said polymer latexprior to fusion of said latex into a film or coating from about 0.5 toabout 5 percent by weight of latex polymer solids of a polyoxyethylenesorbitan fatTy acid monoester containing from about 10 to 20 moles ofethylene oxide and wherein said fatty acid contains from about 12 to 18carbon atoms.
 3. The process of claim 2 wherein the monomers used in thepreparation of said polymer latex are vinylidene chloride, acrylonitrileand sodium sulfoethyl methacrylate.
 3. ANY REMAINDER BEING ONE OR MOREMONOETHYLENICALLY UNSATURATED COMONOMERS SELECTED FROM THE GROUPCONSISTING OF METHACRYLIC ACID, METHYL METHACRYLATE,HYDROXYETHYLACRYLATE, HYDROXYPROPYLACRYLATE, HYDROXYETHYLMETHACRYLATE,ACRYLIC ACID, ACRYLONITRILE, METHACRYLONITRILE, ACRYLAMIDE AND THE LOWEALKYL AND DIALKYLACRYLAMIDES, ACROLEIN, METHYLVINYL KETONE AND VINYLACETATE, SAID PROCESS COMPRISING: HAVING PRESENT IN SAID POLYMER LATEXPRIOR TO FUSION OF SAID LATEX INTO A FILM OR COATING FROM ABOUT 0.5 TOABOUT 5 PERCENT BY WEIGHT OF LATEX POLYMER SOLIDS OF A POLYOXYETHYLENESORBITAN FATTY ACID MONOESTER CONTAINING FROM ABOUT 10 TO 20 MOLES OFETHYLENE OXIDE AND WHEREIN SAID FATTY ACID CONTAINS FROM ABOUT 12 TO 18CARBON ATOMS.
 4. The process of claim 3 wherein said polymer latex isprepared from a monomer composition of about 92 parts by weightvinylidene chloride, about 8 parts by weight acrylonitrile and fromabout 1.4 to 1.6 parts by weight sodium sulfoethyl methacrylate.
 5. Theprocess of claim 3 wherein said polymer latex is prepared from a monomercomposition of about 80 parts by weight vinylidene chloride, about 15parts by weight butyl acrylate, about 5 parts by weight acrylonitrileand about 1.6 parts by weight of sodium sulfoethyl methacrylate.